Lift mechanism for vehicle suspensions

ABSTRACT

A suspension system which includes at least one beam, a support spring extending between the vehicle frame and the support beam and a lift spring extending between a lift bracket welded to the beam and the vehicle frame. The support spring is precompressed by using a U-bolt and may be adjusted by increasing or decreasing the length of the U-bolt. Additionally, the spring provides a constant effective force throughout the entire path of travel of the tire-wheel assemblies attached to the axle. While the axle force provided by the spring increases, the force operates through a changing lever arm relative to the pivot point to assure that the spring force operating through the lever arm remains substantially constant throughout the path of travel of the suspension system.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to an improved suspension system forland vehicles. More particularly, the invention relates to trailing beamair suspension systems. Specifically, the invention relates to a liftmechanism for trailing beam air suspension systems.

2. Background Information

With the advent following World War II of large load carrying capacitytrucks and trailers in this country, came the need to provide add-onaxles for increasing the capacity of trucks over that of the chassis-cabdesign which is manufactured with a limited number of axles. Whileadd-on axles effectively increase load-carrying capacity, it was soonrealized that as the number of load bearing axles increased on a givenvehicle, a number of difficulties arose. Specifically, tire scuffing,loss in fuel economy and the inability to safely corner, all workproblems associated with add-on type axles. Mitigation of these problemswas a primary concern to the industry, which concern results in thedevelopment of the liftable axle suspension system. Such a suspensionsystem could be selectively raised from the road surface or lowered intoengagement with the road surface when needed, thereby mitigating theaforementioned problems.

The transportation of goods by trucks continues to be a primary methodof moving goods from one location to another. This commercial success isdue to the large volume and load-carrying capacity available in standardtrailers as well as the highway system which reaches virtually everypart of North America. However, in order to assure that all manufacturedtrailers will travel easily on existing and newly constructed highways,trailer sizes have been standardized. Specifically, regulations havebeen passed which limit the trailer length, width and height. In aneffort to increase the volume of the trailers, trailer manufacturersroutinely dimension their trailers at the legal limit.

The use of large volume trailers amplifies the need for lift axles to bepositioned under the trailer as the trailers themselves are able tocarry more volume, and consequently, more weight. However, the distancebetween the trailer body and the road surface is relatively limited, andtherefore lift axle suspensions must be manufactured to simultaneouslypermit the tire-wheel assemblies to move into and out of engagement withthe road surface, while mounted to the trailer body.

Similarly, as the need continues to grow for the inexpensive andreliable transportation of goods, so does the popularity of road-railersuspensions such that the trailer may be supported on the trailersuspension, or alternatively on a fixed height rail bogey. A rail bogeygenerally includes a frame which supports at least two rail car wheelsrotatably mounted on an axle. The upper portion of the frame includes alatching mechanism which is complementary related to a similar latchingmechanism on the underneath of the trailer such that the trailer may beraised up via a road-railer suspension, positioned over the rail bogey,and lowered into engagement with the latching mechanism thereon. Theaxle of the road-railer suspension is then raised out of engagement withthe railroad surface, with the rail bogey providing the suspension andwheels for use on railroad tracks.

Road-railer suspensions utilize a lifting mechanism which can either bean air spring, or a mechanical spring of the leaf or coil variety. Theconventional axle lifting mechanism provides one or more stressedmechanical springs acting directly between the vehicle frame and axle.When air is relieved from the air springs, the mechanical springs raisethe axle. The mechanical springs, in their condition of diminishedstress when the axle is fully raised, must still exert sufficient forceto support the weight of the axle and associated tires such that thetires remain in the raised position. When the air springs arepressurized, the wheels are forced downwardly into ground engagementovercoming the load forces and mechanical lift spring forces. In theroad-railer application, the axle is moved between three separatepositions: a first ground engaging position when the road-railersuspension is operating in the highway mode, a second ground engagingposition, or transfer mode, when the trailer is raised to engage a railbogey in coupling mode, and a rail mode where the trailer is supportedon a rail bogey and the tires are lifted out of ground engagingposition.

The lift mechanism must support not only the weight of the axle andwheels, but something greater than that weight in order to assure thatif the rail suspension should encounter an irregularity in the tracksurface, the suspended tire-wheel assemblies do not operate under theincreased force and bounce downwardly to come into contact with thetrack surface and cause significant damage to the suspension system andassociated trailer. Still further, the spring must be of sufficient sizeto assure that as the spring deflection decreases, the spring forceremains sufficiently high to retain the related suspension system in thechosen position. Hooks Law requires that as spring deflection decreases,so does the force provided by that spring. Conversely, as springdeflection increases, so does the force exerted by that spring. Priorart suspensions, while presumably adequate for the purpose for whichthey are intended, often provide much greater force at certain loci ofthe suspension travel than required and a minimum of force at otherpositions along the suspension path of travel. As such, the springmechanism must be manufactured larger than necessary in order to providethe minimum required force to the suspension system at all locationsalong the suspension system path of travel. By so doing, the liftmechanism is necessarily larger and more costly than would otherwise berequired if a constant force at an appropriate level was required at allloci along the suspension system path of travel.

More particularly, Hooks Law requires that as spring deflectionincreases, so does the force exerted by that spring. As such, a smallermore economical lift mechanism may be utilized if the suspension systemprovides a relatively constant force to the suspension at all loci alongthe suspension system path of travel. This need is especially importantwhen a spring lift mechanism is utilized with a trailing or leading beamtype suspension which travels along an arc thereby moving not onlyvertically, but translating longitudinally as it moves from a groundengaging to a non-ground engaging position. Still further, thelongitudinal movement of the axle is substantially increased when atrailing beam is utilized in a road-railer application given therelatively long path of travel of the axle as the suspension moves fromthe coupling mode, when the suspension is fully inflated, to transportmode when the suspension is fully deflated and the tire-wheel assembliesare in a non-ground engaging position.

Leading and trailing beam type suspensions include a pair oflongitudinally extending beams which may be either flexible or rigid,one of which is located adjacent each of two longitudinally extendingslider rails located beneath the body of the truck or trailer. Thesebeams are pivotally connected at one end to a hanger bracket extendingdownwardly from the frame, with an axle extending between the beamsadjacent the other end. Additionally, an air or coil spring is generallypositioned intermediate each frame rail and a corresponding beam. Thebeam may extend forwardly or rearwardly of the pivot, thus defining aleading or trailing beam suspension respectively.

Trailing beam suspension systems have been utilized for many years asthey offer roll stability and may be tailored to create a roll flexibleor roll rigid suspension system and are relatively simple to manufactureand easy to install. However, prior lift mechanisms utilized withtrailing beam suspension systems have been difficult to install, andrelatively expensive to manufacture given that the lift mechanism mustoperate through a relatively large longitudinal axle translation giventhat the trailing beam suspension rotates through an arc about a singlepivot point.

The need thus exists for a lift mechanism for a suspension system or atrailing or leading beam suspension system which provides a relativelyconstant force through the entire path of travel of the axle at a forcesufficient to support the suspension at every location along its path oftravel. Additionally, the need exists for a lift mechanism which issimple to install and easy to manufacture.

SUMMARY OF THE INVENTION

Objectives of the invention include providing a lift mechanism for avehicle suspension system which is simple to manufacture and easy toinstall.

Another objective is to provide a lift mechanism for a suspension systemwhich may be utilized with most suspension systems.

Still another objective is to provide a lift mechanism for a suspensionsystem which utilizes a precompressed coil spring.

Still a further objective of the invention is to provide a liftmechanism for a suspension system which provides a relatively constantforce along the entire path of travel of the associated axle.

Still a further objective is to provide a lift mechanism for asuspension system which may be positioned at any location radially aboutthe lift beam without affecting the force deflection ratio.

A still further objective is to provide such a lift mechanism which isof simple construction, which achieves the stated objectives in asimple, effective and inexpensive manner, and which solves problems andsatisfies needs existing in the art.

These and other objectives and advantages of the invention are obtainedby the improved lift mechanism for a suspension system, the generalnature of which may be stated as including a pivot having a first lineof action; a suspension frame; at least one beam pivotally mounted tothe suspension frame on the pivot; and a lift spring having a force, alength and a second line of action attached to the beam whereby thefirst line of action and the second line of action are spaced apart afirst distance, and in which the first distance increases as the lengthof the lift spring increases, and in which the first distance decreasesas the length of the lift spring decreases.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the invention, illustrative of the best modein which applicant has contemplated applying the principles, is setforth in the following description and is shown in the drawings and isparticularly and distinctly pointed out and set forth in the appendedclaims.

FIG. 1 is a side elevational view of the suspension system of thepresent invention shown attached to a vehicle and with a tire-wheelassembly shown in dot-dash lines, and with portions broken away andshown in section;

FIG. 2 is an enlarged perspective view of the suspension system shown inFIG. 1 with portions broken away;

FIG. 3 is a sectional view taken along line 3--3, FIG. 1;

FIG. 4 is a side elevational view of the suspension system shown in FIG.1 in transfer mode and with portions broken away and in section;

FIG. 5 is a side elevational view of the suspension system shown in FIG.1 in highway mode and with portions broken away and in section;

FIG. 6 is a side elevational view of the suspension system shown in FIG.1 in transfer mode and with portions broken away and in section; and

FIG. 7 is a side elevational view of the suspension system shown in FIG.1 with portions broken away and in section and with the lift mechanismrotated radially relative to the central pivot.

Similar numerals refer to similar parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The improved lift mechanism of the present invention is indicatedgenerally at 1 and is particularly shown in FIGS. 1 and 2 attached to asuspension system 2. Lift mechanism 1 and suspension system 2 are showngenerally in FIGS. 1 and 2, and are particularly adapted to be mountedon a vehicle 3, such as a truck or trailer. Vehicle 3 includes a cargobox 4 supported by a pair of frame rails 5 extending longitudinallybeneath vehicle 3. Suspension system 2 includes a suspension frame 6welded to a pair of slide channels 7. Slide channels 7 are spaced aparta distance equal to the distance between slider rails 5 and are mountedto slider rails 5 with a plurality of mounting pins 8. Suspension system2 further includes an axle 10 supporting a tire-wheel assembly 11 oneach end thereof. Still referring to FIG. 1, suspension system 2includes a central beam 15 and a pair of parallel and spaced apartcontrol arms 16. A pair of air springs 17 extend intermediate centralbeam 15 and slide channels 7.

Referring to FIG. 2, suspension frame 6 includes a front plate 20 and arear plate 21 parallel to and spaced apart from front plate 20. A pairof parallel and spaced apart hanger brackets 22 are positionedintermediate front plate 20 and rear plate 21 adjacent each end thereof.Each pair of plates 22 are positioned apart a distance substantiallyequal to the width of slide channels 7 such that slide channels 7 may bewelded thereto as shown specifically in FIG. 1. Additionally, eachhanger bracket 22 is formed with an axially aligned hole 24 in the lowerrear corner thereof, and one control arm 16 is mounted within holes 24via a pivot pin 25. A pair of parallel and spaced apart pivot flanges 26are positioned intermediate front plate 20 and rear plate 21 forpivotally supporting center beam 15 via a pivot pin 27. Each of frontplate 20 and rear plate 21 are formed with a plurality of holes 28 forreducing the weight thereof.

A pair of parallel and spaced apart inner walls 30 extends between pivotflanges 26 and is welded thereto. Additionally, two pair of parallel andspaced apart cross walls 31 extend between inner walls 30 and aresubstantially perpendicular thereto. Each cross wall 31 is formed with anotch 32 centered along its upper edge for receiving a respective U-bolt33 having a central rod 34 and a pair of parallel and spaced apartthreaded legs 35 which extend substantially perpendicular to central rod34. Additionally, inner walls 30 and cross walls 31 define a pair ofspring boxes 36 for receiving a coil spring 37 therein. Each cross wall31 includes a mounting flange 38 extending away from spring box 36 andformed with a hole 40. Hole 40 is sized to receive one leg 35 of aU-bolt 33.

Referring to FIGS. 2-4, a lift bracket 42 extends forward of centralbeam 15 having a lift bracket or weldment 43 pivotally attached theretovia a mounting bolt 44. Lift weldment 43 includes a spring plate 45 anda pair of parallel and spaced apart downwardly extending mountingflanges 46 welded thereto. Pivot bolt 44 extends through mountingflanges 46 to provide pivotal movement between lift weldment 43 and liftweldment 43. Still further, coil spring 37 is positioned within springbox 36 and on top of spring plate 45 of lift weldment 43.

Each U-bolt 33 extends over a pair of cross walls 31 and is supportedwithin associated notches 32. The ends 50 of legs 35 of each U-bolt 33are threaded and extend through holes 40 formed in mounting flanges 38.Each threaded end 50 receives a lock washer 51 and a nut 52. Nut 52 istightened to compress coil spring 37 to provide a preselected strengthin accordance with Hooks Law. Further, a top weldment 53 is positionedon top of each coil spring 37 and intermediate coil spring 37 and U-bolt33 and provides a force plate 54 and a bolt receiver 55 complementaryshaped to a horizontal portion 56 of U-bolt 33. More particularly, boltreceiver 55 provides an upwardly arcuate section complementary shaped tothe exterior of horizontal portion 56 of U-bolt 33 which is centrallypositioned on force plate 54 to provide a constant downward force ontoU-spring 37. As can be seen from a review of FIGS. 3-4, nuts 52 may betightened along ends 50 of U-bolts 33 in order to increase thedeflection of coil spring 37 thereby assuring that coil springs 37provide an increased moment on central beam 15. Alternatively, nuts 52may be moved downwardly along threaded ends 50 of U-bolt 33 in order todecrease the moment applied to lift bracket 42 and consequently tocentral beam 15 without departing from the spirit of the presentinvention, and in order to provide a simple adjustment to the forceapplied by coil springs 37.

Lift mechanism 1 is shown with a central beam suspension system 2,however, it should be understood from a review of FIGS. 1-4, liftmechanism 1 may be utilized with a traditional trailing beam typesuspension without departing from the spirit of the present invention.

Referring specifically to FIG. 4, suspension system 2 includes a firstline of action A which passes through the center of coil spring 37 anddirectly through mounting bolt 44, and a second line of action Bextending directly through pivot pin 27. First line of action A andsecond line of action B are spaced apart by a distance C which, in thepreferred embodiment, is substantially equal to the length of liftbracket 42. Still further, axle 10 is spaced apart from pivot pin 27 andconsequently from second line of action B a distance indicated at D inFIG. 4. Axle 10 and the associated tire-wheel assemblies are acted uponby gravity such that the effective weight of axle 10 relative to thesecond line of action B equals the weight of axle 10, and the associatedtire-wheel assemblies acting through lever arm, or distance D.Similarly, spring 37 provides an effective force which may be defined asthe force provided by coil spring 37 acting through lever arm, ordistance C. As can be seen from a review of FIG. 4, when moments aresummed about pivot pin 27, the effective force of spring 37 must equalthe effective weight of axle 10 for suspension system 2 to remain in astatic position. More particularly, the force exerted by spring 37, whenmultiplied through lever arm or distance C provides a moment which mustequal the weight of axle 10 and the tire-wheel assemblies mountedthereon multiplied by lever arm, or distance D. When the effective forceof spring 37 is equal to the effective weight of axle 10, suspensionsystem 2 will remain static. However, when suspension system 2 andtire-wheel assemblies 11 are in the raised position as shown in FIG. 4,the effective force of spring 37 must be greater than the effectiveweight of axle 10 as spring 37 must retain suspension system 2 in theraised position even when abrupt downward force is applied to suspensionsystem 2, such as, for example, when vehicle 3 rides over a bump in arail track, or when other tire-wheel assemblies attached to vehicle 3travel over a depression in the road surface. As such, while suspensionsystem 2 weighs in the range of from 1200 to 1600 pounds, spring 37provides an effective force in the range of from 1600 to 2500 pounds,and more particularly in the range of from 1900 to 2300 pounds, and morespecifically spring 37 provides a constant effective force throughoutthe entire path of travel of tire-wheel assembly 11 of approximately2100 pounds.

As should also be apparent from a review of FIG. 4, as spring 37 iscompressed, by increasing the stored potential energy within spring 37in accordance with Hooks Law, lever arm C or the distance between theline of action of spring 37 A and the line of action of pivot bolt 27 Bdecreases. Conversely, as spring 37 moves from a deflected to anon-deflected position, lever arm, or distance C increases. In essence,spring 37 is so positioned that as the potential energy stored withinspring 37 and therefore such that spring 37 may provide an increasedforce, lever arm C decreases to compensate for the increase in forceprovided by spring 37. Similarly, as the amount of force exerted byspring 37 decreases in accordance with Hooks Law as the percentage ofdeflection of spring 37 decreases, lever arm C is larger such that thesmaller force acts through a greater distance about pivot pin 27 inorder to keep the effective force about pivot pin 27 relativelyconstant. In essence, the force exerted by spring 37 is inverselyproportional to the decrease in the length of lever arm or distance Csuch that the moment applied about pivot pin 27 by spring 37 remainsrelatively constant along the entire arc or path of travel of tire-wheelassemblies 11.

Conversely, as the tire-wheel assembly moves from the non-groundengaging position shown in FIG. 4 to the ground engaging position shownin FIG. 5, distance A decreases as axle 10 translates longitudinally asit passes through an arc.

A similar relationship exists between the force exerted by spring 37 andthe lever arm through which the weight of axle 10 and tire-wheelassemblies 11 act relative to pivot pin 27. Specifically, as thedeflection of spring 37 increases, the distance D between axle 10 andpivot pin 27 decreases. The weight of axle 10 and tire-wheel assembles11 thus operate through a smaller lever arm relative to pivot pin 27.Still further, as spring 37 relaxes and lever arm C increases, so doesdistance D between pivot pin 27 and axle 10. Referring to FIG. 4 then,when tire-wheel assembly 11 is in the fully raised position, spring 37remains precompressed to provide a downward force onto lift bracket 42through a distance C. Similarly, the weight of axle 10 operates undergravity through a distance D relative to pivot pin 27 such that theforce provided by spring 37 acting through distance C is greater thanthe weight of axle 10 acting through distance D.

When tire-wheel assemblies 11 are moved to the position shown in FIG. 5,spring 37 is compressed when compared to the position shown in FIG. 4,and, similarly, distance C has been substantially decreased such thatthe increased force of spring 37 operates through a smaller lever arm Cthereby assuring that the force operating through distance C issubstantially equal in both FIGS. 4 and 5. However, distance C does notdecrease at a rate exactly proportional to the increase in the force ofspring 37 which difference is compensated for by the fact that axle 10operates through a smaller distance D relative to pivot pin 27 therebyassuring that spring 17 needs only the same force, and not more force tokeep tire-wheel assemblies 11 in the ground engaging position.

Still further, when the suspension system is in coupling mode as shownin FIG. 6, spring 37 is nearly fully compressed and both distances C andD are relatively small. Inasmuch as the force provided by spring 37 isvery large when suspension system 2 is in the position shown in FIG. 6,it need only operate through a small lever arm C to provide sufficientforce to keep axle 10 operating through a small distance D in thecoupling mode.

As can be seen from a review of FIGS. 4, 5 and 6, the effective force ofspring 37 is substantially constant throughout the path of travel oftire-wheel assemblies 11 given that distances C and D decrease as theforce exerted by spring 37 in accordance with Hooks Law increases. Thepresent invention thus provides a method for providing a relativelyconstant force for moving an axle between a ground engaging and anon-ground engaging position by providing a coil spring which operatesin accordance with Hooks Law by providing additional force as the springis deflected, but assuring that the suspension system is manufactured toprovide a smaller lever arm through which the increased force operatessuch that the smaller lever arm compensates for the increased force witha net result that the lift mechanism provides a relatively constantforce to the suspension system throughout the path of travel of thetire-wheel assemblies. Still further, the suspension system provides aU-bolt for retaining the spring in a precompressed position which issimple to install, and easy to adjust.

Accordingly, the improved lift mechanism for vehicle suspensions issimplified, provides an effective, safe, inexpensive, and efficientdevice which achieves all the enumerated objectives, provides foreliminating difficulties encountered with prior devices, and solvesproblems and obtains new results in the art.

In the foregoing description, certain terms have been used for brevity,clearness and understanding; but no unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art, because suchterms are used for descriptive purposes and are intended to be broadlyconstrued.

Moreover, the description and illustration of the invention is by way ofexample, and the scope of the invention is not limited to the exactdetails shown or described.

Having now described the features, discoveries and principles of theinvention, the manner in which the improved lift mechanism for vehiclesuspensions is constructed and used, the characteristics of theconstruction, and the advantageous, new and useful results obtained; thenew and useful structures, devices, elements, arrangements, parts andcombinations, are set forth in the appended claims.

I claim:
 1. The suspension system for use on a vehicle having a framecomprising:a pivot having a first line of action; a lift bracketattached to the pivot; a suspension frame; at least one beam pivotallymounted to the suspension frame on the pivot; and a lift spring having aforce, a length and a second line of action attached to the beam wherebythe first line of action and the second line of action are spaced aparta first distance, and in which the first distance increases as thelength of the lift spring increases, and in which the first distancedecreases as the length of the lift spring decreases, whereby the liftspring is carried by the lift bracket, and the lift spring expands whenthe lift bracket moves in one direction, and the lift spring compresseswhen the lift bracket moves in a second direction opposite the firstdirection.
 2. The suspension system as defined in claim 1 in which thebeam extends away from the pivot in a first direction, and the liftbracket extends away from the beam in a second direction which differsfrom the first direction.
 3. The suspension system as defined in claim 2in which an axle is carried by the beam; in which the axle is spacedapart from the first line of action a second distance, and in which thesecond distance increases as the spring lift length increases, and thesecond distance decreases as the spring lift length decreases.
 4. Thesuspension system as defined in claim 3 in which the second distance isinversely proportional to the force of the spring lift.
 5. Thesuspension system as defined in claim 3 in which the axle has a path oftravel, in which the spring has an effective spring force measured asthe force of the lift spring acting through the first distance, and inwhich the effective spring force is substantially constant throughoutthe axle path of travel.
 6. The suspension system as defined in claim 3in which the first distance is inversely proportional to the spring liftforce.
 7. The suspension system as defined in claim 6 in which a supportspring is adapted to be positioned intermediate the beam and the frame;in which the support spring moves between a fully expanded and a fullycollapsed position; in which the first distance is largest when thesupport spring is in the fully collapsed position, and the firstdistance is smallest when the support spring is in the fully expandedposition; and in which the force is largest when the first distance issmallest and the force is smallest when the first distance is largest.8. The suspension system as defined in claim 7 in which the supportspring includes at least one air spring.
 9. The suspension system asdefined in claim 6 in which the axle has a ground engaging position anda non-ground engaging position; in which the axle has an effectiveweight whereby the effective weight is measured as the weight measuredat the axle acting through the second distance; and in which theeffective force is at least as large as the effective weight when in thenon-ground engaging position.
 10. The suspension system as defined inclaim 9 in which the effective weight decreases as the force of thespring lift decreases.
 11. The suspension system as defined in claim 9in which the effective weight decreases as the first distance decreases.12. The suspension system as defined in claim 3 in which the effectivespring force is in the range of from 1600 to 2500 pounds.
 13. Thesuspension system as defined in claim 12 in which the effective springforce is in the range of from 1900 to 2300 pounds.
 14. The suspensionsystem as defined in claim 12 in which a spring plate is carried by thelift bracket, and in which the lift spring rests on the spring plate,and in which a force plate is carried by the suspension frame.
 15. Thesuspension system as defined in claim 14 in which the lift spring ispositioned intermediate the spring plate and the force plate.
 16. Thesuspension system as defined in claim 15 in which the lift spring is acoil spring.
 17. The suspension system as defined in claim 1 in whichthe lift spring is a coil spring, and in which a coil spring compressionmeans for compressing the coil spring is positioned adjacent the coilspring.
 18. The suspension system as defined in claim 17 in which thecoil spring compression means includes a rod extending over the coilspring, and compression means for moving the rod toward and away fromthe spring bracket when positioned over the coil spring.
 19. Thesuspension system as defined in claim 18 in which means for moving therod includes a pair of bolts extending downwardly from the rod on eitherside of the coil spring, and a nut whereby movement of the nut relativeto the bolt in a first direction moves the rod away from the liftbracket, and movement of the nut relative to the bolt in a seconddirection opposite the first direction causes the rod to move toward thespring lift bracket.
 20. The suspension system as defined in claim 19 inwhich a flange is carried by the suspension frame on either side of thecoil spring, and in which one bolt extends through each flange, and thenut is carried by the bolt on the opposite side of the flange as therod.
 21. The suspension system as defined in claim 20 in which the boltsextend substantially parallel with the second line of action.
 22. Thesuspension system as defined in claim 20 in which the bolt and rods areintegrally connected to form a U-shaped bolt.
 23. The suspension systemas defined in claim 22 in which the suspension frame includes a squarehousing, and in which the lift means is carried within the squarehousing.
 24. The suspension system as defined in claim 23 in which thesquare housing is formed with a pair of notches for retaining theU-shaped bolt over the lift spring.